The old two wrongs make a right argument? 
Two wrongs don't make a right if the two wrongs aren't related. I can't punch your grandmother just because you punched me. Two wrongs make a right when they are directly connected. Say you stole $200 bucks from me on Sunday and on Monday I steal it back. Well you owe me $200, so call it two wrongs or whatever you'd like, but in my book its ok.